This invention relates to medical devices, and more particularly to methods of manufacturing and coating medical devices utilizing thermal spray processing and cold spray processing. The medical devices may be made porous to act as a functional drug delivery vehicle.
Several interventional treatment modalities are presently used for heart disease, including balloon and laser angioplasty, atherectomy, and by-pass surgery. A focus of recent development work in the treatment of heart disease has been directed to endoprosthetic devices referred to as stents. Stents are generally cylindrically shaped intravascular devices that are placed within an artery to hold it open. The device can be used to reduce the likelihood of restenosis and to maintain the patency of a blood vessel immediately after intravascular treatment. In some circumstances, a stent can also be used as the primary treatment device where the stent is expanded to dilate a stenosis and then left in place.
Many medical devices, including stents, are manufactured from commercially available metals and metal alloy substrates, such as stainless steel and cobalt based alloys, configured as tube stock, wherein the substrate typically has average grain sizes ranging from approximately 0.0025 inch (64 microns), ASTM grain size 5, to around 0.00088 inch (22 microns), ASTM grain size 8. These grain sizes typically result in about two to five grains across the thickness of the device. Part of the limitation in achieving a finer grain size with metals and metal alloys arises from the number of draws and anneals the substrate must go through to achieve its final size. Stents and other medical devices (such as guide wires, ring markers, pacemaker lead tips, and catheters) may benefit from a reduction in grain size of the substrate.
Intravascular interventional devices, such as stents, are typically implanted within a vessel in a contracted state, and expanded when in place in the vessel in order to maintain the patency of the vessel. Such medical devices may have a metallic support structure to provide the strength required to maintain the patency of the vessel in which it is to be implanted so as to allow fluid flow through the vessel. Such metallic medical devices are often provided with an exterior surface coating with the purpose of providing a more biocompatible and/or hemocompatible surface. Since it is often useful to provide localized therapeutic pharmacological treatment of a blood vessel at the location being treated with the medical device, it has been the practice within the medical industry to configure such implantable medical devices with a coating of a polymeric material having the capability of being loaded with antiproliferative drugs and other therapeutic agents. Such polymer coated medical devices provide for the placement and release of therapeutic drugs at a specific intravascular site, but are relatively expensive and difficult to manufacture using conventional processes.
What has been needed and heretofore unavailable in the art of manufacturing medical devices, such as stents, configured from commercially available biocompatible materials, such as stainless steel and cobalt-based alloys, are methods for forming porous implantable medical devices and for forming a porous coating on consolidated medical devices. In addition, it would be desirable to form drug-eluting medical devices without the need for coating the substrate with a polymer. The present invention meets these and other needs.